Depending upon the time in the bag, the metabolism and size of the fish, the total available ammonia, TAM, called NHx here, level can be very high. We have measured in excess of 30 ppm. If the NHx level is very high in the shipping water, and in the form of NH4+ it is relatively harmless. But it can become exceptionally lethal immediately upon opening the shipping bag. As the water with high NHx content is exposed to the atmosphere the pH of the shipping water will change very quickly, converting a large part of the NHx will become NH3. This will burn the fishes gills
• It is important to remember that changes in shipping water changes the pH in the animals blood and this takes time to adjust too, which is one of the factors for this
• So one must be very careful in acclimation to avoid exposing the animal to NH3 or shocking the animal with too rapid a change in pH while the animal’s blood pH is reduced. Here is a good study if anyone wants to read it. It points out a lot of science based info and general observations on acclimation.
http://www.sustainableaquatics.com/docs/Acclimation-White-Paper.docx